Subtle brain dysfunction in treated 6-pyruvoyl-tetrahydropterin synthase deficiency: relationship to motor tasks and neurophysiological tests

Two Cases of 6-Pyruvoyl Tetrahydropterin Synthase Deficiency: Case Report and Literature Review

6-pyruvoyl tetrahydropterin synthase deficiency (PTPSD) is a rare neurometabolic disease that can be diagnosed in newborn screening (NBS) and is part of the family of tetrahydrobiopterin deficiency disorders (BH4Ds). It is essential to diagnose and treat this disease early to prevent permanent neurological damage secondary to this neurotransmitter disorder. We present the first two cases of PTPSD in Romania that were genetically confirmed and treated late. Improving the diagnosis and monitoring procedures in Romania with correct metabolic management will prevent severe neurological impairment from PTPSD or other BH4Ds.

Potential involvement of the microbiota-gut-brain axis in the neurotoxicity of triphenyl phosphate (TPhP) in the marine medaka (Oryzias melastigma) larvae

Triphenyl phosphate (TPhP), a prevalent pollutant in the aquatic environment, has been reported to induce neurotoxicity (e.g., a suppression in locomotor activity) in fish larvae, posing a great threat to fish populations. However, the underlying mechanism was not fully revealed. In this study, the Oryzias melastigma larvae (21 dph) were exposed to waterborne TPhP (20 and 100 μg/L) for 7 days and a decreased locomotor activity was found. After exposure, the brain transcriptome and communities of gut microbiota were investigated to explore the potential mechanism underlying the suppressed locomotor activity by TPhP. The results showed that 1160 genes in the brain were dysregulated by TPhP, of which 24 genes were identified as being highly associated with the neural function and development (including nerve regeneration, neuronal growth and differentiation, brain ion homeostasis, production of neurotransmitters and etc), suggesting a general impairment in the central nervous system. Meanwhile, TPhP caused disorders in the gut microbiota. The relative abundance of Gammaproteobacteria and Alphaproteobacteria, which can influence the brain functions of host via the microbiota-gut-brain axis, were significantly altered by TPhP. Furthermore, the Redundancy analysis (RDA) revealed positive correlations between the intestinal genera Ruegeria, Roseivivax and Nautella and the dysregulated brain genes by TPhP. These results suggest that TPhP might impair the central nervous system of the O. melastigma larvae not only directly but also through the microbiota-gut-axis (indirectly), contributing to the suppressed locomotor activity. These findings enrich our mechanistic understanding of the toxicity of TPhP in fish larvae and shed preliminary light on the involvement of microbiota-gut-brain axis in the neurotoxicity of environmental pollutants.

6-Pyruvoyltetrahydropterin Synthase Deficiency: Review and Report of 28 Arab Subjects

BACKGROUND

Tetrahydrobiopterin is an essential cofactor for the hydroxylation of aromatic amino acids phenylalanine, tyrosine, and tryptophan. Therefore, tetrahydrobiopterin deficiency results in hyperphenylalaninemia as well as dopamine and serotonin depletion in the central nervous system. The enzyme 6-pyruvoyltetrahydropterin synthase catalyzes the second step of de novo synthesis of tetrahydrobiopterin, and its deficiency is the most frequent cause of tetrahydrobiopterin metabolism disorders.

METHOD

We conducted a retrospective chart review of 28 subjects from 24 families with molecularly confirmed 6-pyruvoyltetrahydropterin synthase deficiency from six centers in three Arab countries. We reviewed clinical, biochemical, and molecular data. We also reviewed previously published cohorts of subjects with 6-pyruvoyltetrahydropterin synthase deficiency.

RESULTS

Similar to previous observations, we show that early treatment (less than two months) is associated with better outcome. We identify eight PTS variants in 24 independent families. The most common variant is (c.238A>G; p.M80V) with an allele count of 33%. We also identify one novel variant (c.2T>G; p.?).

CONCLUSION

The deficiency of 6-pyruvoyltetrahydropterin synthase is relatively common in the Arab population and should be considered in individuals with hyperphenylalaninemia. More natural history studies with comprehensive biochemical and molecular genetics data are needed for a robust base for the development of future therapy.

A case of 6-pyruvoyl-tetrahydropterin synthase deficiency demonstrates a more significant correlation of L-Dopa dosage with serum prolactin levels than CSF homovanillic acid levels

6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is a tetrahydrobiopterin (BH4) deficiency that presents as hyperphenylalaninemia. Administration of the neurotransmitter precursors L-Dopa/carbidopa and 5-hydroxytryptophan (5HTP), as well as BH4, is necessary for treatment. It has been reported that serum prolactin levels are elevated in patients with PTPS deficiency indicating that inhibition of prolactin secretion by dopamine is insufficient and is negatively correlated with the CSF level of HVA. Here, we present a case of PTPS deficiency which showed a more significant correlation of dosage of L-Dopa/carbidopa with serum prolactin levels than with CSF HVA levels. Combined treatment of BH4, L-Dopa/carbidopa, and 5HTP was started as the CSF neopterin/biopterin ratio (N/B ratio 7.54, control 0.46-1.59) and serum prolactin level (36.79 ng/ml, control <15) were elevated. The dosage of L-Dopa/carbidopa was adjusted in the range of 9.08-10.5mg/kg/day. The CSF level of HVA stayed within normal limits using these dosages of L-Dopa/carbidopa, and there was no correlation between dose given and HVA level (R=0.230, p=0.71). On the other hand, even in this relatively small dosing range, the serum prolactin level showed significant negative correlation with the dosage of L-Dopa/carbidopa (R=0.645, p=0.023). The patient did not show any neurological symptoms even when the serum prolactin level was elevated. From these results, we suggest that the serum prolactin level may be a more sensitive marker than the CSF HVA level to guide the dose adjustment of L-Dopa/carbidopa in the management of patients with PTPS deficiency.

Long-term follow-up and adult outcome of 6-pyruvoyl-tetrahydropterin synthase deficiency

Little information is available on the long-term course and adult outcome of patients with 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. We describe the course of a 32-year-old woman with hypotonia, dystonia, choreoathetosis, mental retardation, behavioral disturbances, and incomplete puberty due to PTPS deficiency. From the age of 6 months she developed progressive hypotonia and choreoathtetoid movements despite good control of hyperphenylalaninemia. Tetrahydrobiopterin deficiency was diagnosed at age 3 years. She had a dramatic response to L-dopa, which persisted at a stable dose for 29 years. Reducing the L-dopa dose led to severe axial hypotonia and limb dystonia, and increasing it led to florid abnormal movements and behavioral disorders. This report illustrates the role of dopamine modulation in motor, psychiatric, and endocrine functions.